Steps to Tame a high level Desmodus with 100% Effektiveness (you need a low level Desmodus to start) :
Step 1: Tame a Stego/Andrewsarchus and saddle them (the saddle on the Andrew is essential!)
Step 2: Tame a Moschops of any level
Step 3: Farm 400-600 Bloodpacks
Step 4: After finding your target Desmodus take out your Stego/Andrewsarchus and your Moschops
Step 5: Put all the Bloodpacks except for the last 100 in the Moschops (the other 100 you keep in your own inventory)
Step 6: put the Moschops on "Following: Lowest" and let it follow your Andrew/Stego
Step 7: Aggro the Desmodus by approaching it and let it grab the moschops, the Desmodus will eat 10 Bloodpacks from the Moschops' inventory and then drop it, this will raise its Effectiveness by 1-3% (repeat this until the Desmodus is at 100% Effectivness. Do not unmount while doing this!)
Step 8: once the Desmodus is at 100% Effectiveness unmount and offer yourself up to the Desmodus. It will grab you and eat 10 Bloodpacks and then drop you.
Step 9: after it dropped you immediately mount your Andrew/Stego again. And let it grab the Moschops again so it's Effectiveness goes back up to 100%
Step 10: Repeat Step 8 & 9 until the Desmodus is tamed.
Latitude:38 Longitude:75, inside a cave under a waterfall
Latitude: 90 Longitude: 78, cave as well
Latitude: 50 Longitude: 14, cave
Use a Daedon, put meat inside, set to passive, passive healing on and kill all the other desmodus until there is only one, then duck under the Daedon and the desmodus will grab it, suck it's blood and the effectiveness will go up 3-4%, don't leave the area, hide and wait until 100%. Once 100% effectiveness, let it grab you (make sure you have 150-200 blood packs) and you'll tame it. Use cryopods if possible to bring back the Daedon.
You Need A Blood Extaction Sryringe Then Get Blood From You DONT Drink It Go In A Trench Or A Cave If You See A Hanging Pod On The Roof A GIANT Bat Will Come Out Wait For It To Pick You Up Then Have The Blood Packs In Your Inventory Becuse It Will Drink The Blood Packs And The Tameing Bar Will Fill Up When It Drinked ALL Of The Blood Packs And It’s Not Tamed You HAVE To Get Some More Blood From Your Character And It Will Keep Drinking Them But You MIGHT Be LOW On Health.
Try to tame a low level one first so you can farm blood packs with it, it'll shorten the farming time for a high level bat.
You can also tame a Daeodon first and use it's healing aura when extracting the first few packs, the pig can also help you raise the taming effectiveness for future high level tames, just let it wander on passive near the Desmodus you want to tame, keep some blood packs on it's inventory and let it get picked, it'll raise the effectiveness.
Let it pick you afterwards and feed on your blood packs to raise the taming meter, when it's about to tame, be sure to check if the effectiveness is close to 100%, if not just let it pick the Daeodon some more.
It can turn invisible at night and while it is latched upside down during both night and day. Every time it bites a creature, it adds blood packs to it's inventory, making it good to use to tame bloodstalkers. It collects tons of spoiled meat when it eats corpses making it also good for narcotic farming. It has echolocation which allows it to ping all nearby creatures, and finally it has the ability to dive similar to the griffin and snow owl. It's tamed passively by putting blood packs in the last slot of your hotbar and letting it pick you up.